1. Field of the Invention
Exemplary aspects of the present invention generally relate to an image forming apparatus, such as a copier, a facsimile machine, a printer, or a multi-functional system including a combination thereof, and more particularly, to an optical writing unit and an image forming apparatus including same.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image bearing member; an optical writer projects a light beam onto the charged surface of the image bearing member to form an electrostatic latent image on the image bearing member according to the image data; a developing device supplies toner to the electrostatic latent image formed on the image bearing member to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image bearing member onto a recording medium or is indirectly transferred from the image bearing member onto a recording medium via an intermediate transfer member; a cleaning device then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the unfixed toner image to fix the unfixed toner image on the recording medium, thus forming the image on the recording medium.
Typically, an electrophotographic image forming apparatus forms an electrostatic latent image on a photoconductive drum using an optical writing unit that illuminates the photoconductive drum with a light beam. As a light source for the light beam, the optical writing unit includes a light emitting element (LED) array head consisting of a plurality of light emitting elements, for example, light emitting diodes aligned in a certain direction. Based on image data signals, lighting of each LED is controlled, and the projected light is focused onto the photoconductive drum through a lens array, thereby writing the electrostatic latent image on the surface of the photoconductive drum.
In such an image forming apparatus, when a write controller that controls projection of light from the LED array head transfers the image data signal to the LED array head, radiated electric field noise is generated in the signal line which can cause adjacent instruments to malfunction. For this reason, the level of an electromagnetic interference (EMI) needs to be suppressed within a permissible level.
In view of the above, a known optical writing unit employs a regulator to reduce a swing level of the image data signals, thereby reducing the level of EMI generated in the signal line from the write controller to the LED array head.
Another known approach to reducing the level of EMI uses a spread spectrum technique to transfer the image data signal and an image data transfer clock signal.
Although advantageous and generally effective for their intended purpose, there is a drawback to the known approaches in that the swing level of the image data signal drops, thus degrading a signal-to-noise (S/N) ratio of the image data signal upon transfer. As a result, the quality of the image data signal is degraded.
In a case in which the image data signal and the image data transfer clock signal are transferred using the spread spectrum technique, in order to drive four LED heads, energy four times greater than when driving a single LED head is radiated. Consequently, even when the image data signal and the image data transfer clock signal for each LED head is spread, the EMI level still spikes.
Therefore, there is a demand for an optical writing unit that can reduce the EMI level upon transfer of the image data signal without degrading the S/N ratio.